1. Field of the Invention
The present invention relates generally to a solar cell with a conductive base and to a method of manufacturing the same.
2. Related Background Art
Thin-film solar cells with metal substrates can be used for various purposes due to their characteristics of using light and flexible substrates. Furthermore, the metal substrates can withstand high-temperature processing. In view of this, the improvement in conversion efficiency of the solar cells can be expected.
When using a conductive substrate, there is a problem in that it is difficult to connect a plurality of unit cells in series on the substrate and thus to obtain an integrated structure. In addition, when using a metal sheet as a substrate, a constituent element contained in the metal sheet diffuses into a light-absorption layer and thus the characteristics are deteriorated, which also is a problem. In order to solve such problems, a method has been disclosed that includes forming an insulating layer on a metal substrate and forming an electrode layer and an amorphous Si layer as a light-absorption layer thereon (for instance, JP 05(1993)-129641 A and JP 11(1999)-261090 A).
On the other hand, solar cells using semiconductors having a chalcopyrite structure, which are represented by Cu(In, Ga)Se2 (hereinafter referred to as xe2x80x9cCIGSxe2x80x9d), for the light-absorption layer have high conversion efficiency and thus are receiving much attention. Generally, in the solar cells using CIGS, glass substrates are used as the bases. In addition, solar cells also have been reported in which polyimide or stainless steel sheets are used instead of the glass substrates for the purpose of manufacturing lightweight or flexible solar cells.
In solar cells using semiconductors (of chalcopyrite structure) including at least one element from each of groups Ib, IIIb, and VIb, further improvements in reliability and characteristics have been requested.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a solar cell with good characteristics and high reliability using a semiconductor including at least one element from each of groups Ib, IIIb, and VIb, and to provide a method of manufacturing the same.
In order to achieve the above-mentioned object, a first solar cell according to the present invention includes: a conductive base; a first insulating layer formed on one principal plane of the base; a second insulating layer formed on a second principal plane of the base; and a light-absorption layer disposed above the first insulating layer. The light-absorption layer is formed of a semiconductor including at least one element from each of groups Ib, IIIb, and VIb. The first solar cell can avoid the base being embrittled by reacting with the group VIb element (particularly, Se or S) when the light-absorption layer is formed. Therefore, a solar cell with good characteristics and high reliability can be obtained. In addition, it also can be avoided that the productivity decreases due to a chalcogenide compound produced by the reaction between the group VIb element and the base. Furthermore, in the first solar cell, the insulating layer can prevent an element contained in the base from diffusing into the light-absorption layer. This effect is particularly important when the base is formed of metal.
Throughout this specification, xe2x80x9cgroups Ib, IIIb, VIb, and Iaxe2x80x9d refer to xe2x80x9cgroups 1B, 3B, 6B, and 1Axe2x80x9d of the periodic table of elements according to the old IUPAC recommendation before 1985. Thus, a xe2x80x9cgroup Ib elementxe2x80x9d, xe2x80x9cgroup IIIb elementxe2x80x9d, xe2x80x9cgroup VIb elementxe2x80x9d, and xe2x80x9cgroup Ia elementxe2x80x9d denote one of a series of elements containing Cu, one of a series of elements containing Al, Ga, and In, one of a series of elements containing S, Se, and Te, and one of a series of elements containing Li, Na, and K, respectively.
The first solar cell further may include a plurality of unit cells connected in series on the first insulating layer. According to this configuration, an integrated solar cell with a large area and good characteristics can be obtained.
In the first solar cell, the base may be formed of metal, and the semiconductor may contain Cu, at least one element selected from a group consisting of In and Ga, and at least one element selected from a group consisting of Se and S. When a thin base is used in the above-mentioned configuration, a flexible solar cell can be obtained. In addition, the use of the metal base allows processing at a high temperature to be carried out and thus allows a light-absorption layer to be formed of a semiconductor with especially high crystallinity.
In the first solar cell, the base may be formed of stainless steel or an aluminum alloy. According to this configuration, a lightweight solar cell can be obtained.
The first solar cell further may include a conductive layer formed on the first insulating layer and a layer A disposed between the conductive layer and the light-absorption layer. The layer A may contain a group Ia element. According to the above-mentioned configuration, a solar cell with excellent characteristics can be obtained.
In the first solar cell, the group Ia element may be Na.
In the first solar cell, the first and second insulating layers have a mean thickness of not more than 0.5 xcexcm. According to the configuration described above, the substrate surface is allowed to have uniform temperature distribution when the light-absorption layer is formed. In addition, the base and the conductive layer can be prevented from coming off.
In the first solar cell, the first and second insulating layers may be formed of at least one selected from a group consisting of oxide and fluoride.
In the first solar cell, the first and second insulating layers essentially may consist of silicon oxide. According to the configuration described above, the base and the conductive layer can be prevented from coming off. Furthermore, the insulating layers can be formed easily.
In the first solar cell, the first and second insulating layers essentially may consist of iron fluoride. According to this configuration, uniform insulating layers can be formed easily.
A second solar cell according to the present invention includes: a conductive base; an insulating layer formed on the base; a conductive layer formed on the insulating layer; and a light-absorption layer disposed above the conductive layer. At least one layer disposed between the base and the light-absorption layer contains a group Ia element. The light-absorption layer is formed of a semiconductor including at least one element from each of groups Ib, IIIb, and VIb. According to the second solar cell, a solar cell with good characteristics and high reliability can be obtained. Conceivably, this is because the crystallinity of the light-absorption layer is improved by the group Ia element contained in the layer disposed between the base and the light-absorption layer. Furthermore, in the second solar cell, the insulating layer can prevent an element contained in the base from diffusing into the light-absorption layer. This effect is particularly important when the base is formed of metal.
The second solar cell further may include a plurality of unit cells connected in series on the insulating layer.
In the second solar cell, the base may be formed of metal, and the semiconductor may contain Cu, at least one element selected from a group consisting of In and Ga, and at least one element selected from a group consisting of Se and S.
In the second solar cell, the base may be formed of stainless steel or an aluminum alloy.
In the second solar cell, the insulating layer may contain the group Ia element.
In the second solar cell, the insulating layer may be formed of an oxide containing Na.
In the second solar cell, the insulating layer may be formed of soda-lime glass.
In the second solar cell, the insulating layer may be formed of NaF.
The second solar cell further may include a layer B disposed between the conductive layer and the light-absorption layer. The layer B may contain a group Ia element.
In the second solar cell, the layer B may be formed of Na2S or NaF.
A method of manufacturing a solar cell with a conductive base according to the present invention includes: (i) forming, on the base, a multilayer film including a conductive layer and a layer containing a group Ia element; and (ii) forming, on the multilayer film, a light-absorption layer formed of a conductor including at least one element from each of groups Ib, IIIb, and VIb. According to the manufacturing method described above, a light-absorption layer with excellent crystallinity can be formed. Therefore, a solar cell with good characteristics and high reliability can be obtained.
In the method of manufacturing a solar cell, the base may be formed of metal, and the semiconductor may contain Cu, at least one element selected from a group consisting of In and Ga, and at least one element selected from a group consisting of Se and S.